Carbon can exist in many forms which differ in their physical form and properties, including diamond/sp3 carbon. Diamond-like carbon is typically an amorphous form of sp3 carbon and has many of the same properties of diamond. Diamond-like carbon has short order chains rather than the long order chains of natural diamonds. Diamond-like coatings on substrates are used in a range of industries due to their hardness, wear resistance, high conductivity of heat, high degree of chemical inertness and low coefficient of friction.
A number of methods have been developed to deposit diamond-like coatings on a substrate, such as sputtering processes, ion beam and plasma RF deposition processes, using AC or pulsed DC voltages, using gaseous or solid carbon sources and applying sublayers to the substrate before depositing diamond-like coatings or using composite carbon coatings. Prior art methods are only capable of creating coatings up to about 5 microns without flaking. Examples of these methods can be found in WO2005/056869, WO03/078679, WO99/27893, and WO2005/054540.
RU2094528 describes a method of sputtering to obtain a diamond-like coating on a substrate. This document discloses pumping hydrocarbon into a chamber having two cathodes, an anode and the substrate, where one of the cathodes is a graphite cathode. Carbon atoms are sputtered in all directions, originating from both the hydrocarbon gas and the graphite cathode. This indirect coating method suffers from poor adhesion and deposition rates and poor deposition uniformity occurs when coating larger objects.
RU2095466 describes using an alternating magnetic field, and a hydrocarbon gas as the sole carbon source to deposit a diamond like coating directly onto the substrate. This method allows larger and circular objects to be coated and increases the deposition rate of the coating. However, due to the non-linear magnetic field a non-uniform magnetic field is created and therefore an even coating is not obtained.
RU2105082 discloses a two step method in which a sublayer is applied to the substrate before the diamond-like coating is applied, which increases the adhesion of the diamond-like coating. The document describes placing Ti cathodes between the anode and the object to be coated to sputter Ti onto the surface of the substrate. Once the sublayer is formed, the Ti cathode voltage is changed to become an anode, sputtering is stopped, and hydrocarbon gas is then introduced to form the diamond-like coating on the substrate. However the Ti electrode interferes with plasma flow during the diamond-like coating step, causing poor deposition rates and uneven coatings, especially on larger articles.